imback82 commented on a change in pull request #30881:
URL: https://github.com/apache/spark/pull/30881#discussion_r549528750
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveSessionCatalog.scala
##########
@@ -235,8 +236,17 @@ class ResolveSessionCatalog(
case DescribeRelation(ResolvedV1TableOrViewIdentifier(ident),
partitionSpec, isExtended) =>
DescribeTableCommand(ident.asTableIdentifier, partitionSpec, isExtended)
- case DescribeColumn(ResolvedV1TableOrViewIdentifier(ident), colNameParts,
isExtended) =>
- DescribeColumnCommand(ident.asTableIdentifier, colNameParts, isExtended)
+ case DescribeColumn(ResolvedV1TableOrViewIdentifier(ident), column,
isExtended) =>
+ column match {
+ case u: UnresolvedAttribute =>
+ // For views, the column will not be resolved by `ResolveReferences`
because
+ // `ResolvedView` stores only the identifier.
+ DescribeColumnCommand(ident.asTableIdentifier, u.nameParts,
isExtended)
+ case a: Attribute =>
+ DescribeColumnCommand(ident.asTableIdentifier, a.qualifier :+
a.name, isExtended)
+ case nested =>
+ throw
QueryCompilationErrors.commandNotSupportNestedColumnError("DESC TABLE COLUMN")
Review comment:
One disadvantage of this approach is that the exception message for view
will be different when nested column is specified; it will have the original
name parts:
https://github.com/apache/spark/blob/0617dfce7beb34662ab30a607721e9b46e65c21e/sql/core/src/main/scala/org/apache/spark/sql/execution/command/tables.scala#L773
We can do one of the following:
* Make the exception message the same even for views by dropping column name
in `DescribeColumnCommand`
* Store the original column name in `DescribeColumn` (and there will be no
matching logic for column in `ResolveSessionCatalog`, but seems duplicated
because we have `UnresolvedAttribute` to store the original column name.)
* Construct the original name from `GetStructField`, `GetArrayStructFields`,
etc.
WDYT, @cloud-fan ?
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